Why are my car cooling fans not coming on?

The cooling fans are supposed to kick in to protect the engine from overheating and to aid the radiator and A/C condenser. In most cars, a handful of common issues—electrical faults, faulty sensors or switches, a failing fan motor, or a control-system fault—prevent the fans from engaging. Low coolant can also play a role. This guide explains the main causes and practical steps to diagnose and address the problem.

Quick checks you can perform at home

These checks cover the simplest and most likely causes. They help you rule out easy fixes before deeper diagnostics or a trip to a shop.

• Check fuses and relays: Open the under-hood fuse box and inspect the fuse(s) labeled for the radiator fans (often marked FAN or FANS). If a fuse is blown, replace it with one of the same rating. Swap the fan relay with a similar relay from another circuit to test whether the relay is faulty.


• Inspect fan connectors and grounds: Look for loose, corroded, or damaged connectors at the fan(s). Ensure the ground strap to the engine block or chassis is clean and tight.


• Test power at the fan when the engine is warm and the A/C is on: With the engine at normal operating temperature and the A/C set to MAX, the fans should receive 12V at the connector. If there’s no power, the issue lies upstream (fuse/relay, wiring, or ECU command).


• Check coolant level and leaks: Low coolant can affect sensor readings and the cooling system’s ability to reach the right temperature for fan operation. Top up if needed and inspect for leaks.


• Look for obstruction or damage: Debris in front of the radiator or damaged fan blades can prevent proper operation or cooling performance.

If these checks don’t reveal the cause, note the symptoms (when the fans should turn on, whether both fans engage, and whether the A/C affects them) and move to more in‑depth diagnostics or seek professional help.

Electrical sensors and control modules that commonly fail

The engine management system relies on sensor data and control modules to decide when to run the fans. Faulty inputs or electronics can prevent proper fan operation.

Coolant temperature sensor (ECTS)

The ECTS feeds the ECU with coolant temperature data. If it reads incorrectly (too hot or erratic), the ECU may delay or fail to command the fans, or it may overcool the engine.

High‑temperature switch and dedicated fan switch

Some vehicles use a separate switch that directly powers the fans at a set temperature. A faulty switch can prevent the fans from engaging even when the engine is hot.

Fan control module or ECU/PCM

Many modern cars use a dedicated fan controller or the ECU/PCM to drive the fans. A malfunction, software fault, or blown fuse in this circuit can stop fan operation and may trigger codes in the onboard computer.

Wiring and grounds

Damaged insulation, chafed wires near the radiator, or poor grounds can interrupt the circuit or signals to the fan motor, even when other parts seem fine.

Diagnostics often involve checking sensor readings with an OBD-II scanner, inspecting wiring for wear or corrosion, and performing continuity tests. When sensors read out of spec or the ECU reports cooling-related codes, replacement or repair may be necessary.

Mechanical wear and physical issues

Even with a healthy electrical supply, the fan assembly itself can fail or become obstructed, keeping the system from cooling properly.

Fan motor or clutch failure

Electric radiator fans can burn out or jam, while dual-fan configurations may lose one unit. If a fan won’t spin at all or only runs intermittently, the motor or control circuit could be at fault. In cars with a mechanical clutch fan, the clutch can seize or slip, reducing cooling efficiency or preventing the fan from engaging as designed.

Debris, obstruction, or bearing wear

Objects or leaf debris can block the fan blades, and worn bearings can cause excessive play or noise. Either issue can reduce cooling performance or prevent proper operation.

Mechanical issues typically require replacement of the fan assembly or specific components, even if the electrical path remains intact.

When to seek professional help

If basic checks don’t pinpoint the cause or if the car continues to overheat, a professional diagnosis is advised. Trained technicians can perform advanced electrical tests, thermal pressure tests, and wiring inspections with specialized tools.

• Check for diagnostic trouble codes related to cooling, sensors, or fans using an OBD-II scanner.


• Test sensor values and fan duty cycles with a professional scan tool to confirm correct signaling to the fan controller/ECU.


• Evaluate the cooling system as a whole, including coolant quality, pressure, radiator, and hoses, to identify contributing factors.


• Inspect the fan assembly and related wiring for damage or corrosion that may require component replacement.

Because some faults are intermittent or require specialized equipment, a professional assessment is prudent when symptoms persist or if overheating recurs.

Summary

Fueling the answer: cooling fans not coming on is usually due to electrical faults (fuses, relays, wiring), sensor/switch failures (coolant temperature sensor or high‑temperature switch), or control/module issues, with low coolant as a possible contributor. Start with quick at‑home checks of fuses, relays, connectors, and coolant level, then move to sensor and control‑system diagnostics. If symptoms persist or overheating occurs, seek professional evaluation to prevent engine damage and ensure safe operation.

What to do if a car cooling fan is not working?

If your car cooling fan is not working, you should check the fuse, relay, and fan motor, and consider seeking professional assistance if needed.

How to tell if a cooling fan relay is bad?

A bad cooling fan relay can cause symptoms like engine overheating, the cooling fan not turning on when needed, and intermittent fan operation. You can diagnose a faulty relay by checking for these signs, listening for a clicking sound from the relay when the engine is hot, or testing the relay directly using a multimeter. A bad relay can also trigger error codes and affect the performance of your air conditioning. 
This video demonstrates how to swap relays to test if your cooling fan is working: 51sCB7 MediaYouTube · Jul 9, 2022
Common symptoms of a bad cooling fan relay

• Engine overheating: This is a critical sign, as the fan is no longer able to cool the engine effectively. You may see steam or the temperature gauge in the red zone. 
• Cooling fan not operating: The most obvious symptom is that the fan doesn't turn on at all, especially when the engine is hot or when the AC is running. 
• Intermittent or erratic fan operation: The fan may turn on and off randomly, causing fluctuating engine temperatures. 
• Poor A/C performance: A bad relay can impact the air conditioning system, causing it to blow warm air. 
• Blown fuses: A failing relay can sometimes cause electrical issues that lead to a blown fuse in the cooling fan circuit. 
• Error codes: On modern vehicles, a bad relay can trigger an error code on your dashboard, notes ancel. 

How to test a cooling fan relay 
You can watch this video to learn how to test a cooling fan relay with a multimeter: 58sCarsNToysYouTube · Aug 6, 2017

• Listen for the relay: With the engine warm, have a helper turn the A/C on or let the engine idle until it's hot. Listen for a distinct "click" from the relay when the fan is supposed to turn on. 
• Swap with an identical relay: If your car has an identical relay for a non-essential system (like the horn or power windows), you can try swapping them. If the fan starts working and the other system stops, the relay is bad. 
• Use a multimeter: 
  • Check resistance: With the relay removed, set your multimeter to the ohms setting and test the resistance between the coil pins (usually labeled 85 and 86). A good relay should have a specific resistance (often between 50-120 ohms, but check your vehicle's specs). 
  • Check continuity: You can also use a multimeter to check for continuity between the power and switch contacts when the relay is energized, say ancel and PartSouq. 

This video shows how to test a fan relay using a 9V battery: 1mDrive - Chris CapredoniYouTube · Aug 12, 2024

Can I still drive if my radiator fans are not working?

No, you should not drive with a radiator fan not working, as it can quickly lead to engine overheating and cause severe, expensive damage. While the car can still run, it risks major engine problems like a blown head gasket or warped cylinder heads. If you must drive, do so for the shortest possible distance while closely monitoring the temperature gauge and pulling over immediately if it overheats. 
Risks of driving with a broken radiator fan

• Engine overheating: The fan is crucial for cooling the engine, especially at low speeds or while stopped in traffic. Without it, the engine can overheat very quickly. 
• Severe engine damage: Overheating can cause critical and costly damage to your engine, such as a blown head gasket or warped cylinder heads. 
• Over-pressurization: Driving with the A/C on can over-pressurize the A/C system, which may cause refrigerant to be released. 

How to minimize risk if you absolutely must drive

• Drive only the necessary distance: The goal is to get the vehicle to a mechanic as quickly as possible. 
• Monitor the temperature gauge: Keep a constant eye on your engine temperature gauge and pull over immediately if it gets too hot. 
• Turn on the heater: Turn the cabin heat to the maximum setting. This uses the engine's heat to help cool it down. 
• Avoid stop-and-go traffic: Try to avoid situations where you will be stopped for extended periods. 
• Turn off the A/C: This will prevent additional strain on the cooling system. 

What would cause radiator fans to not turn on?

A radiator fan may not be working due to electrical issues like a blown fuse or faulty relay, problems with the temperature sensor, or physical issues with the fan motor, blades, or wiring. Less common causes include a low coolant level or a broken fan clutch, which could also lead to engine overheating. 
This video demonstrates the symptoms of a bad radiator fan, including a check engine light, poor AC performance, and a lack of fan noise: 59sEasyAutoFixYouTube · Jun 27, 2022
Electrical problems

• Blown fuse: This is a very common cause, as the fan motor can draw a lot of current. Consult your car's manual to find and replace the fuse if it's blown. 
• Faulty relay: A bad relay can prevent power from reaching the fan motor. You can sometimes test a relay by swapping it with a similar one from the fuse box. 
• Wiring issues: Damaged, broken, or corroded wires and connectors can cut off power to the fan. Inspect all connections between the fan, relay, and control unit. 

Sensor and control problems

• Faulty temperature sensor: The fan relies on a sensor to know when to turn on. If this sensor fails, it can prevent the fan from activating. 
• Malfunctioning control module: In some cases, a computer control module (ECM) could be the source of the problem. 

Physical or mechanical problems

• Failed fan motor: The motor itself can burn out over time. You can test this by applying a direct power source (like from the car battery) to the fan's connector to see if it spins. 
• Broken fan clutch: This applies to fans that are mechanically driven by the engine, not electric fans. 
• Damaged fan blades: Bent or broken blades can cause the fan to catch on other components. 

Other potential issues

• Low coolant level: Insufficient coolant can cause the engine to overheat, which might damage the fan or cause sensors to malfunction. 
• Air in the cooling system: Trapped air can interfere with proper heat distribution and sensor function. 

This video demonstrates how to test the fan motor directly with a power source: 1mCB7 MediaYouTube · Jul 15, 2022
If you've checked the fuse and relay and still can't identify the problem, it's best to consult a mechanic to avoid further damage or safety hazards.